Radio communication system, communication terminal apparatus, base station apparatus, and transmission power control method

ABSTRACT

The present invention relates to a radio communication system comprising base stations and mobile stations and a method for controlling transmission power in the system where the base station is able to perform multi-point transmission for transmitting the same signal to a plurality of the mobile stations. In the present invention, the mobile station targeted for the multi-point transmission provides the base station of an increase request or a decrease request of the transmission power by respectively transmitting or not transmitting a predetermined signal to the base station.

TECHNICAL FIELD

The present invention relates generally to transmission power control ina radio communication system adapted for the Code Division MultipleAccess (CDMA) method (hereinafter referred to merely as a “CDMA radiocommunication system”), and more particularly to a method and apparatusfor controlling the transmission power in which a mobile station uses acode sequence assigned separately for each multi-point transmissiongroup to provide a base station of its transmission power controlrequest in the CDMA radio communication system adapted for multi-pointtransmission where the base station transmits the same signal to aplurality of mobile stations.

BACKGROUND ART

As known widely, in the CDMA radio communication system, it isindispensable to perform the transmission power control (especially inuplinks) in order to reduce interference.

In a conventional CDMA radio communication system, the mobile stationdetermines whether to request the base station to increase or decreasethe transmission power on the basis of receiving quality of signals fromthe base station, and then transmits a transmission power control signalrepresenting an increase request or a decrease request to the basestation.

An example of such processing is shown in FIG. 1. Each mobile stationdetermines whether the receiving quality is good or not by comparing itwith a predetermined threshold, and then transmits the transmissionpower control signal representing the decrease request when thereceiving quality exceeds the threshold, while it transmits one thatrepresents the increase request when the receiving quality is lower.

The base station, which receives such transmission power control signal,controls its transmission power used for the sending mobile station ofthat transmission power control signal in accordance with the increaseor decrease request that is represented in the received signal.

In the conventional CDMA radio communication system, a spreading code isassigned separately for each mobile station. For example, in the exampleshown in FIG. 1, signals transmitted from Mobile Station #1 are spreadby Code #1, while ones from Mobile Station #2 are spread by Code #2.

In such case where a separate spreading code is assigned for each mobilestation, orthogonality among the spreading codes becomes weak and theinterference increases in the uplink when the number of the mobilestations increases and hence the number of the spreading codes requiredincreases.

DISCLOSURE OF THE INVENTION

It is an object of the present invention to provide the method andapparatus for controlling the transmission power that solve theabove-mentioned problem when the CDMA radio communication systemperforms multi-point transmission.

Here, multi-point transmission means a transmission method fortransmitting the same signal from a single base station to a pluralityof the mobile stations at a time, and is considered to be employed in,for example, a multicast information distribution service that hasrecently become widely watched.

The above object is achieved by a radio communication system comprisingbase stations and mobile stations where the base station is able toperform multi-point transmission for transmitting the same signal to theplurality of the mobile stations, wherein the mobile station targetedfor the multi-point transmission provides the base station with theincrease or decrease request of the transmission power by transmittingor not transmitting a predetermined signal to the base station.

Here, the above-mentioned predetermined signal may be an arbitrary bitsequence, for example.

Other objects, features, and advantages of the present invention areelucidated in the following detailed description with reference to theaccompanied figures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram showing a state of the conventional transmissionpower control;

FIG. 2 is a schematic of a base station according to a first embodimentof the present invention;

FIG. 3 is a schematic of a mobile station according to the firstembodiment of the present invention;

FIG. 4 is a diagram showing a state of transmission power controlaccording to the first embodiment of the present invention;

FIG. 5 is a schematic of a base station according to a second embodimentof the present invention;

FIG. 6 is a schematic of a mobile station according to the secondembodiment of the present invention;

FIG. 7 is a diagram showing a state of transmission power controlaccording to the second embodiment of the present invention;

FIG. 8 is a schematic of a mobile station according to a thirdembodiment of the present invention;

FIG. 9 is a schematic of a base station according to the thirdembodiment of the present invention;

FIG. 10 is a schematic of a correlation detecting part of the basestation according to the third embodiment of the present invention;

FIG. 11 is a diagram showing an example of the relationship between PNcode sequences and amounts of control of the transmission power;

FIG. 12 is a diagram showing an example of the amount of controlrequested from a mobile station belonging to the multi-pointtransmission group;

FIG. 13 is a schematic of a mobile station according to a fourthembodiment of the present invention;

FIG. 14 is a schematic of a mobile station according to a fifthembodiment of the present invention;

FIG. 15 is a schematic of a correlation detecting part of a base stationaccording to the fifth embodiment of the present invention;

FIG. 16 is a flowchart showing a flow of a correlation detecting processaccording to the sixth embodiment of the present invention; and

FIG. 17 is a flowchart showing a flow of a correlation detecting processaccording to the seventh embodiment of the present invention.

PREFERRED EMBODIMENTS FOR CARRYING OUT THE INVENTION

The embodiments of the present invention are described hereinafter withreference to the accompanying drawings.

The method for controlling the transmission power according to the firstembodiment of the present invention is now described with reference toFIGS. 2 through 4. In this embodiment, the spreading code assignedseparately for each multi-point transmission group is used as therequest signal transmitted from the mobile station to the base stationin the transmission power control, and the increase or decrease requestis identified by transmitting or not transmitting the request signal.

First, the configuration and operation of the mobile station and thebase station according to this embodiment are described with referenceto FIGS. 2 and 3. FIG. 2 is the schematic of the multi-pointtransmitting base station in the CDMA radio communication systemaccording to this embodiment, and FIG. 3 is the schematic of the mobilestation targeted for the multi-point transmission in the CDMA radiocommunication system according to this embodiment. In both figures, onlyportions that are necessary for illustrating the present invention areoutlined, and showing and detailing known configurations or functionsare omitted.

In the base station 200, a multi-point transmitted signal is input froma signal input terminal 201 and modulated at a modulating part 202. Thismodulation is a so-called narrow-band modulation such as QPSK and 16QAM.A modulated signal to be transmitted, of which the transmission power iscontrolled by a variable transmission power amplifier 203, is thentransmitted via an antenna 204 to the plurality of target mobilestations 300 of the multi-point transmission at a time. The transmissionpower control by the variable transmission power amplifier 203 isperformed as directed by a later-mentioned transmission powercontrolling part 207.

In each mobile station 300, the multi-point transmitted signal from thebase station 200, which is received by an antenna 301, is demodulated bya demodulating part 302, and then output to a signal output terminal 303and a receiving quality measuring part 304.

A demodulated signal, of which the receiving quality is measured by thereceiving quality measuring part 304, is then determined whether torepresent the increase or decrease request of the transmission power tothe base station by comparing the result of such measurement with apredetermined threshold.

Here, the receiving quality may be determined using any parameters. Forexample, receiving power, carrier power to noise power ratio (C/N),signal power to noise power ratio (S/N), carrier power to sum ofinterference power and noise power (C/(I+N) ), signal power to sum ofinterference power and noise power (S/(I+N)), bit error rate (BER)likelihood obtained in error correction decoding, and any combination ofthese may be used.

The receiving quality measuring part 304 outputs a transmission powercontrol signal representing the increase or decrease request to a switch305 on the basis of the above determination. The switch 305 is closedwhen the transmission power control signal input represents the increaserequest, while it is opened when it represents the decrease request.

A code generating part 306 keeps generating a predetermined single codesequence. Therefore, only when the transmission power control signalrepresenting the increase request is input to the switch 305, thepredetermined code sequence is then output to the modulating part 307.Here, the predetermined single code sequence is the code sequence thatis assigned separately for each multi-point transmission group and hencethat is unique to the group.

The request signal, which is the predetermined single code sequence andis input to the modulating part 307, is moderated, and then transmittedto the base station 200 via the antenna 301. This modulation is alsonarrow-band modulation.

An example of the request signal is shown in FIG. 4. FIG.4 is based onthe same transmission path condition as one shown in FIG. 1. As shown,in each mobile station, the request signal is transmitted only when thereceiving quality is lower than the predetermined threshold and hencethe mobile station requests the base station to increase thetransmission power.

On the other hand, in the base station 200, the request signal in thetransmission power control from the multi-point transmission targetmobile station 300, which is received by the antenna 204, is demodulatedby a demodulation part 205 and is output to a request signal detectingpart 206.

The request signal detecting part 206 compares a value of the receivedelectric power of the demodulated signal with a predetermined threshold.Since the request signal from the multi-point transmission target mobilestation 300 is, as described above, transmitted to the base station onlywhen the mobile station requests to increase the transmission power, itis determined that there are some mobile stations that transmit therequest signal when the value exceeds the above threshold and that thereis no mobile station that transmits the request signal when it does notexceed.

A result of the determination whether the request signal is detected inthe request signal detecting part 206 is output to the transmissionpower controlling part 207. When the request signal is detected, thetransmission power controlling part 207 directs the variabletransmission power amplifier 203 to increase the transmission power of amulti-point transmission signal for the benefit of the mobile stationthat is one of the multi-point transmission target mobile stations andof which the receiving quality is not good. When the request signal isnot detected, it is considered that all multi-point transmission targetmobile stations receive the multi-point transmission signal with goodenough receiving quality, and the transmission power controlling part207 directs the variable transmission power amplifier 203 to decreasethe transmission power. Here, the amount of control to decrease orincrease one time may be any value.

Thus, according to this embodiment, in the transmission power control inthe multi-point transmission, the increase or decrease request isprovided from the mobile station to the base station by transmitting ornot transmitting the predetermined code sequence assigned separately foreach multi-point transmission group. Therefore, when there are somemobile stations in the multi-point transmission group of which thereceiving quality is not good, the transmission power of the multi-pointtransmission signal can be controlled, and the increase of interferencein the uplink can be prevented when the number of the mobile stationsincreases.

Here, in this embodiment, assuming that the code sequence output fromthe code generating part 306 is a code sequence that consists ofsequential “1”s, a detection method that uses electric power measurementwith unmodulated signals can be utilized in the base station 300. Inother words, the above-mentioned code sequence is not limited to thespreading code, and may be a signal that consists of a predetermined bitsequences.

Also, in this embodiment, the above-mentioned code sequence, which istransmitted as the request signal, may be transmitted after it is spreadwith another spreading code, as well as in the usual CDMA communication.In other words, this embodiment can be directly applied to the existingCDMA communication system.

Furthermore, since it is not required for this embodiment to perform thespreading process, this embodiment can be also applied to communicationsystems adapted for TDMA and FDMA methods.

The transmission power controlling method according to the secondembodiment of the present invention is now described with reference toFIGS. 5 through 7. In this embodiment, the increase or decrease requestfor transmission power to the base station is identified by spreading ornot spreading the transmission power control signal transmitted to thebase station from the mobile station in the transmission power controlwith the spreading code assigned separately for each multi-pointtransmission group.

First, the configuration and operation of the base station and themobile station according to this embodiment are described with referenceto FIGS. 5 and 6, respectively. FIG. 5 is the schematic of themulti-point transmitting base station in the CDMA radio communicationsystem according to this embodiment, and FIG. 6 is the schematic of themulti-point transmission target mobile station in the CDMA radiocommunication system according to this embodiment. In both figures, onlyportions that are necessary for illustrating the present invention areoutlined, and showing and detailing known configurations or functionsare omitted. Also, the same component as one in the already describedembodiment has a consistent reference number, and the detaileddescription of it is omitted.

In the base station 500, a spreading part 501 spreads a modulatedmulti-point transmission signal with the spreading code assignedseparately for each multi-point transmission group.

In each mobile station 600, a despreading part 601 despreads thereceived multi-point transmission signal. And, the transmission powercontrol signal modulated by the modulating part 307 is input to aspreading part 602, while the code sequence output by the codegenerating part 306 is also input thereto only when that transmissionpower control signal represents the increase request of the transmissionpower.

If the code sequence is input, the spreading part 602 transmits thetransmission power control signal to the base station 500 afterspreading it, while, if the code sequence is not input, the spreadingpart 602 transmits the transmission power control signal to the basestation 500 without spreading.

An example of the above-mentioned transmission power control signal isshown in FIG. 7. FIG.7 is based on the same transmission path conditionas one shown in FIG. 1. As shown, in each mobile station, thetransmission power control signal is spread with the code sequenceassigned separately for each multi-point transmission group only whenthe receiving quality is lower than the predetermined threshold andhence the mobile station requests the base station to increase thetransmission power.

In the base station 500, the transmission power control signal receivedfrom the multi-point transmission target mobile station 600 is despreadby the despreading part 502 and is correlated with the code sequenceassigned for that multi-point transmission group.

In the conventional CDMA radio communication system, a transmittingmobile station is identified by the spreading code. However, in thisembodiment, since the mobile stations belonging to the same multi-pointtransmission group use the same code sequence for the sreading processof the transmission power control signal, the transmission power controlsignals for one group are received in a combined form.

Since the despreading process in the despreading part 502 is to performa correlation process on the combined signal, a peak is detected in thedespreading process to the combined signal if there is even one mobilestation that requests to increase the transmission power in thatmulti-point transmission group.

A result of the determination whether the peak is detected or not in thedespreading part 502 is output to the transmission power controllingpart 503. When the peak is detected, the transmission power controllingpart 207 directs the variable transmission power amplifier 203 toincrease the transmission power of the multi-point transmission signalfor the benefit of the mobile station that is one of the multi-pointtransmission target mobile stations and of which the receiving qualityis not good. When the peak is not detected, it is considered that allmulti-point transmission target mobile stations receive a multi-pointtransmission signal with good enough receiving quality, and directs thevariable transmission power amplifier 203 to decrease the transmissionpower. Here, the amount of control to decrease or increase one time maybe any value.

Thus, according to this embodiment, in the transmission power control inthe multi-point transmission, the increase or decrease request isprovided from the mobile station to the base station by spreading or notspreading with the predetermined code sequence assigned separately foreach multi-point transmission group. Therefore, when there are somemobile stations in the multi-point transmission group of which thereceiving quality is not good, the transmission power of the multi-pointtransmission signal can be controlled, and the increase of interferencesin the uplink can be prevented when the number of the mobile stationsincreases.

The transmission power controlling method according to the thirdembodiment of the present invention is now described with reference toFIGS. 8 through 13. This embodiment utilizes basically the sameconfiguration and operation as ones according to the first embodiment,and provides not only the increase or decrease request of thetransmission power but also the request amount of control from eachmobile station to the base station by assigning a plurality ofpredetermined code sequences separately for each multi-pointtransmission group and utilizing the distinctiveness among the set ofcode sequences.

First, the configuration and operation of the mobile station and thebase station according to this embodiment are described with referenceto FIGS. 8 through 10. FIG. 8 is the schematic of the multi-pointtransmission target mobile station 800 in the CDMA radio communicationsystem according to this embodiment, FIG. 9 is the schematic of themulti-point transmitting base station 900 in the CDMA radiocommunication system according to this embodiment, and FIG. 10 is theschematic of the correlation detecting part 901 of the base stationaccording to this embodiment. In each figure, only portions that arenecessary for illustrating the present invention are outlined, andshowing and detailing known configurations or functions are omitted.Also, the same component as one in the already described embodiments hasa consistent reference number, and the detailed description of it isomitted.

As shown, the mobile station 800 according to this embodiment has aplurality of (here, N individual) code generating parts 801, where eachof the code generating parts 801 always keeps outputting differentiablePN codes (PN#1 to PN#N) Each of the N individual PN codes is associatedwith a different value of control of the transmission power in advance.

The set of PN codes is here assigned for different multi-pointtransmission groups. For example, in the case that the number ofavailable PN codes is 256 and that there are four multi-pointtransmission groups, the 1st through 64th PN codes are assigned to the1st group, the 65th through 128th PN codes are assigned to the 2ndgroup, the 129th through 192nd PN codes are assigned to the 3rd group,and the 193rd through 256th PN codes are assigned to the 4th group.

A switch 803 is an (N+1) selector. The switch 803 has N individual inputterminals, one for each code generating part 801, and oneconnection-less terminal 802. The terminals of the switch 803 areselected in accordance with the value of control that is represented bythe transmission power control signal input from the receiving qualitymeasuring part 304.

An example of the operation standard of the switch 803 is shown in FIG.11. It is here assumed that eight kinds of transmission power controlsignals (000 to 111) are input to the switch 803 from the receivingquality measuring part 304 and that five code generating parts 801 areprovided.

As shown, a different transmission power control signal is output fromthe receiving quality measuring part 304 in accordance with the value ofcontrol (dB unit) requested to the base station on the basis of thereceiving quality. It is here assumed that the request value of controlis, as shown, −2 dB to +5 dB.

When the transmission power control signal is input, the switch 803performs one of operations, which are in advance associated with thetransmission power control signals, in accordance with that inputsignal. In this example, when the request value of control is equal toor lower than ±0 dB (that is, when it is not an increase request), theconnection-less terminal 802 is connected (meaning connection-off) andhence the request signal is not output, when +1 dB is requested, thecode sequence PN#1 is used for the request signal, subsequently, inturn, PN#2 for +2 dB, PN#3 for +3 dB, PN#4 for +4 dB, and PN#5 for +5 dBare respectively output to the modulating part 307 and used for therequest signal to the base station.

On the other hand, the base station 900 receives the request signal thatis any one code sequence in the predetermined set of the code sequencestransmitted from each multi-point transmission target mobile station800, and calculates correlation between the receiving signal and theabove-mentioned predetermined set of the code sequences in thecorrelation detecting part 901.

The configuration and operation of the above-mentioned correlationdetecting part 901 is now described with reference to FIG. 10. FIG. 10is the schematic of the correlation detecting part 901 according to thisembodiment. N individual code generating parts 1001, each of whichemploys the same configuration as the code generating part 801 of themobile station side, are provided and output PN codes PN#1 to PN#N,respectively. Each multiplier 1002 calculates complex multiplicationbetween the received signal and complex conjugate of each PN codesequence.

The real part of the complex vector signal obtained by the multiplier1002 is integrated by each integrator 1003. The resultant value of theintegration is determined whether to be equal to or higher than apredetermined threshold or not by the threshold deciding part 1004, andthe result of this decision is recorded in a memory 1005. A result ofdetermination whether there are any mobile stations that request toincrease the transmission power for each amount of control associatedwith the code sequence is thus accumulated in the memory 1005.

A retrieving part 1006 makes reference to the determination resultaccumulated in the memory 1005 to retrieve the largest amount of controlamong the amounts of control requested by the mobile stations and thento output a PN code number associated with the maximum amount of controlto the transmission power controlling part 902.

The transmission power controlling part 902 makes reference to apre-stored relationship (an example of which is shown in FIG. 11)between the PN code and the amount of control (increase) of thetransmission power with input PN code number, and then directs thevariable transmission power amplifier 203 to increase the transmissionpower in accordance with the amount of control of the transmission powerof that PN code.

Also, when no PN code sequence number is input from the correlationdetecting part 901, the transmission power controlling part 902considers that all multi-point transmission target mobile stationsbelonging to that multi-point transmission group receive the multi-pointtransmission signal with good enough receiving quality, and directs thevariable transmission power amplifier 203 to decrease the transmissionpower.

This is now described more specifically with reference to an example ofthe multi-point transmission group shown in FIG. 12. As shown, it isassumed that there is the multi-point transmission group consisting ofsix mobile stations: MS1 through MS6, and that contents of thetransmission power control requested to the base station determined ineach mobile station are MS1:+3 dB, MS2:+2 dB, MS3:+1 dB, MS4:−1 dB,MS5:+2 dB, and MS6:±0 dB, respectively.

In the case of the above example, assuming that the PN code sequencestransmitted from each mobile station to the base station is based on therelationship shown in FIG. 11, PN#3 is transmitted from MS1, PN#2 istransmitted from MS2 and MS5, PN#1 is transmitted from MS3, and no PNcode sequence is transmitted from MS4 or MS6.

Then, since, in the example shown in FIG. 12, +3 dB from MS1 is thelargest request value of control in the amounts of control requestedfrom each mobile station and accumulated in the memory 1005, thetransmission power controlling part 902 directs the variabletransmission power amplifier 203 to increase the transmission power ofthe that multi-point transmission signal by 3 dB.

Thus, according to this embodiment, in the transmission power control inthe multi-point transmission, the increase or decrease request isprovided from the mobile station to the base station by transmitting ornot transmitting the predetermined code sequence assigned separately foreach multi-point transmission group, and also the request amount ofcontrol is provided as well utilizing the distinctiveness among the codesequences used. Therefore, increase of interferences in the uplink canbe prevented when the number of the mobile stations increases, and thetransmission power can be quickly and flexibly controlled in accordancewith the transmission path condition.

Here, in the above description, the case is described that the codesequence is transmitted only when the contents of control requested fromthe mobile station to the base station indicates the increase request.This results so that, when the request to keep or decrease thetransmission power is desired, processing can be advantageouslysimplified, in a view that all mobile stations already receive with goodenough receiving quality. However, of course, the code sequences can beassigned separately for each amount of control in the request to keep ordecrease to provide the base station of it. In this case, since quickcontrol can be also achieved for decreasing, resource efficiency canimprove.

Also, in the description of this embodiment, the PN code is just anexample of the code sequence having distinctiveness, and other spreadingcode having the distinctiveness such as orthogonal Gold code, or errorcorrecting codes such as BCH code, RS code, or M-array code may be used.

Furthermore, in this embodiment, the code sequence, which is transmittedas the request signal, may be spread with another spreading code, aswell as in the usual CDMA communication.

The transmission power controlling method according to the fourthembodiment of the present invention is now described with reference toFIG. 13. This embodiment utilizes basically the same configuration andoperation as ones according to the second embodiment, and provides notonly the increase or decrease request of the transmission power but alsothe request amount of control from each mobile station to the basestation by assigning a plurality of predetermined code sequencesseparately for each multi-point transmission group and utilizing thedistinctiveness among the set of the code sequences as well as the thirdembodiment.

Here, since the base station according to this embodiment is identicalto the base station 900 (FIG. 9) according to the third embodiment,showing and detailing of it are omitted.

FIG. 13 is the schematic of the multi-point transmission target mobilestation 1300 in the CDMA radio communication system according to thisembodiment. In this figure, only portions that are necessary forillustrating the present invention are outlined, and showing anddetailing known configurations or functions are omitted. Also, the samecomponent as one in the already described embodiments has a consistentreference number, and the detailed description of it is omitted.

In the mobile station 1300, as well as the third embodiment, the PN codesequence in accordance with the request value of control is input fromthe switch 803 to a spreading part 1301. The spreading part 1301 spreadsthe transmission power control signal modulated by the modulating part307 with the code sequence output from the switch 803. When thetransmission power control requested to the base station is not theincrease request, the switch 803 turns its input terminal to theconnection-less terminal 802, and hence no code sequence is input to thespreading part 1301, therefore, the transmission power control signal isthen transmitted to the base station without spreading.

In the base station, the same processing as one in the base station 900according to the third embodiment is performed. It is then determinedwhether there are any mobile stations transmitting the increase requestand how large the request amount of control is, and the transmissionpower is increased in accordance with the request amount of control fromthe mobile station having the worst receiving condition.

Thus, according to this embodiment, in the transmission power control inthe multi-point transmission, the increase or decrease request isprovided from the mobile station to the base station by spreading or notspreading with the predetermined code sequence assigned separately foreach multi-point transmission group, and also the request amount ofcontrol is provided as well utilizing the distinctiveness among the codesequences used. Therefore, increase of interferences in the uplink canbe prevented when the number of the mobile stations increases, and thetransmission power can be quickly and flexibly controlled in accordancewith the transmission path condition.

Here, in the above description, the case is described that thetransmission power control signal spread with the code sequence istransmitted only when the contents of control requested from the mobilestation to the base station indicates the increase request. This resultsso that, when the request to keep or decrease the transmission power isdesired, processing can be advantageously simplified, in a view that allmobile stations already receive with good enough receiving quality.However, of course, the code sequences can be assigned separately foreach amount of control in the request to keep or decrease to provide thebase station of it. In this case, since quick control can be alsoachieved for decreasing, resource efficiency can improve.

Also, in the description of this embodiment, the PN code is just anexample of the code sequence having the distinctiveness, and otherspreading code having the distinctiveness such as orthogonal Gold code,or error correcting codes such as BCH code, RS code, or M-array code maybe used.

The transmission power controlling method according to the fifthembodiment of the present invention is now described with reference toFIGS. 14 and 15. This embodiment utilizes approximately the sameconfiguration and operation as ones according to the fourth embodiment,however, the mobile station transmits a predetermined signal, instead ofthe transmission power control signal, to the base station afterspreading it with a selected code sequence. Here, only portions that arenecessary for illustrating the present invention are outlined, andshowing and detailing known configurations or functions are omitted.Also, the same component as one in the already described embodiments hasa consistent reference number, and the detailed description of it isomitted.

FIG. 14 is the schematic of the mobile station 1400 according to thisembodiment. A signal generating part 1401 always keeps outputting apredetermined bit sequence. This bit sequence is spread with the codesequence output from the switch 803 by the spreading part 1301, and isthen transmitted to the base station 1500.

FIG. 15 is the schematic of a correlation detecting part 1501 of thebase station 1500 according to this embodiment. Each of deciding parts1502 decides whether the received signal that is despread with each codesequence is the above predetermined bit sequence output from the signalgenerating part 1401. This decision process is similar to a usual datademodulation. Then, this decision result is recorded in the memory 1005.

Detailed description of the transmission power control processes otherthan those above is omitted since they are similar to the processesaccording to the fourth embodiment. Here, any bit sequence may be usedfor the above predetermined bit sequence.

Thus, according to this embodiment, the predetermined single bitsequence is used for the request signal from the mobile station, and thebase station can utilize the decision using the data demodulationinstead of the decision using the predetermined threshold where itsdetection capability significantly depends on the setting of thethreshold, and thereby it is determined whether that code sequence isused for spreading in the mobile station by double examinationconsisting of the correlation process and the bit decision. Therefore,more reliable and stable correlation detection can be achieved.

The transmission power controlling method according to the sixthembodiment of the present invention is now described with reference toFIG. 16. This embodiment utilizes basically similar configuration andoperation to ones according to the third or fourth embodiment, however,the correlation detector in the base station is implemented by software.

The program processing to implement the correlation detector is nowdescribed with reference to the flow chart shown in FIG. 16. Here, theblock diagram showing the configuration of the base station and themobile station is omitted.

First, 0 is assigned to a variable n in S1601 where n is a variablerepresenting the PN code number. In other words, in S1601, the 0th PNcode is set as the initialized state. It is here assumed that the valueof n is, like the example shown in FIG. 11, set such that it correspondsto the request value of control (dB unit).

A correlation value between the received signal and the 0th PN code isthen calculated in S1602, where X (t) is time-series data of thereceived signal, Xn* (t) is a complex conjugate of the time-series dataof the n^(th) PN code, T is the length of the time-series data, and Γnis the correlation value between the received signal and the n^(th) PNcode.

It is then decided in S1603 whether the correlation value calculated inS1602 is equal to or higher than a predetermined threshold or not. If itis equal to or higher than the threshold, 1 is then assigned to avariable Sn, while, if it does not reach to the threshold, 0 is thenassigned to Sn (S1605), where the variable Sn is a flag that becomes onwhen the correlation value Γn between the received signal and the nth PNcode exceeds the predetermined threshold.

The variable n is then incremented by one (S1606), and it is decidedwhether n reaches N (S1607). If it reaches, the process then proceeds toS1608, while, if it does not, the process then returns to S1602.

In S1608, (N−1) is assigned to the variable n, and the (N−1)th PN codeis set. It is then decided whether the variable n is 1 or not (S1609).If Sn is not equal to 1 (“No” at S1609) n is then decremented one by oneuntil it becomes 0 (S1610 and S1611) to find the value of n when Sn=1.

If it is decided that Sn=1 in S1609, the process then proceeds to S1613and the transmission power is increased by n [dB] on the basis of thevalue of n at that time. Also, if n becomes 0 before it is decided thatSn=1 in S1609 (“Yes” at S1611), it is decided that the correlation valuethat exceeded the predetermined threshold is not obtained. In otherwords, it is determined that th re is no mobile station that requests toincrease the transmission power in that multi-point transmission group.Therefore, the transmission power of the multi-point transmission signalis decreased in S1612.

Thus, according to this embodiment, since the correlation detector canbe implemented by software, the base station according to the presentinvention can have a simplified configuration.

The transmission power controlling method according to the seventhembodiment of the present invention is now described with reference toFIG. 17. This embodiment also has the correlation detector in the basestation implemented by software like the sixth embodiment, howeverutilizes a different algorithm from one used in the processes of thesixth embodiment.

In the correlation detecting process according to the sixth embodiment,the transmission power of the multi-point transmission signal iscontrolled in accordance with the mobile station requesting the largestamount of increase of the transmission power, i.e. the transmissionpower is controlled such that the mobile station having the worsereceiving quality can have good receiving quality.

On the other hand, in this embodiment, putting importance on theefficiency of the whole system, the transmission power is controlled inaccordance with the amount of control that is requested by the mostmobile stations in the amounts of control requested from the mobilestations. By the way, such control is not performed in the conventionalsystem, since the conventional base station individually controls thetransmission power for each mobile station.

The program processing to implement the correlation detector is nowdescribed with reference to the flow chart shown in FIG. 17. Here,detailed description of the variables and the processes used also in theprocess in FIG. 16 is omitted. Also, the block diagram showing theconfiguration of the base station and the mobile station is omitted.

First, S1701 and S1702 are identical to S1601 and S1602 in FIG. 16. Γnis then assigned to the variable Sn in S1703.

Similarly, S1704 and S1705 are identical to S1604 and S1605 of FIG. 16.If n reaches N, the process proceeds to S1706.

Then, (N−1) and S_(N−1) are assigned to n_(max) and Sn_(max)respectively in S1706, where Sn_(max) represents the largest correlationvalue obtained by that time, and n_(max) represents the value of n (i.e.the PN code number) when the largest correlation value is obtained.

It is then decided whether Sn at that time is larger than Sn_(max) ornot in S1707. If Sn at that time does not exceed the largest valueSn_(max) obtained by that time (“No” at S1707), n is then decrementedone by one until it becomes 0 (S1710 and S1711) to find the value of nwhen Sn>Sn_(max).

If Sn is larger than Sn_(max) (“Yes” at S1707), n and Sn at that timeare assigned respectively to n_(max) and Sn_(max) as a new maximum value(S1708). Here, since the request signal or the transmission powercontrol signal from the mobile stations that request the same amount ofincrease consists of the same PN code sequence or is spread with thesame PN code sequence, the request signals from all the mobile stationsthat request the same amount of control are detected in a combined formupon being despread. Therefore, the more the mobile stations thatrequest the same amount of control are, the larger correlation value isobtained. That is, the above comparison of magnitude of the correlationvalue means the comparison of count for each amount of controlrequested.

Then, if n becomes 0 (“Yes” at S1710) and it is determined that thecomparison on Sn is completed for all n, it is decided whether Sn_(max)at that time exceeds the predetermined threshold or not (S1711).

If Sn_(max) exceeds the predetermined threshold (“Yes” at S1711), thetransmission power is increased by n [dB] on the basis of the value of nat that time. For example, in the example shown in FIG. 12, since themobile stations that request +2 dB of increase of the transmission powerare the most, the correlation value on the second PN code sequence PN#2becomes the largest and the transmission power is increased by +2 dB.

Also, if the maximum correlation value Sn_(max) does not exceed thepredetermined threshold in S1711 (“NO” at S1711), it is then determinedthat there is no mobile station that requests increase of thetransmission power in that multi-point transmission group. Therefore,the transmission power of the multi-point transmission signal isdecreased in S1712.

Thus, according to this embodiment, since the transmission power of themulti-point transmission signal is increased on the basis of the amountof control requested by the most mobile stations in the mobile stationsbelonging to the multi-point transmission group, the transmission poweris not excessively increased in consequence of the reduced receivingquality of a particular mobile station, and the transmission power ofthe multi-point transmission signal can be controlled in view of theefficiency in the whole system.

As described above, according to the above first through seventhembodiments, in the transmission power control in the radiocommunication system adapted for the CDMA method, as for the targetmobile station of the multi-point transmission, since the code sequenceis not assigned separately for each mobile station but separately foreach request signal or separately for each request amount of control,the possibility of increase of the interference in the uplink byincreasing the number of the mobile stations can be reduced.

1. A method for controlling transmission power in a radio communicationsystem comprising a base station and a mobile station where the basestation is able to perform multi-point transmission for transmitting thesame signal to a plurality of the mobile stations, wherein: the mobilestation targeted for the multi-point transmission provides the basestation of an increase request or a decrease request of the transmissionpower by respectively spreading or not spreading a transmission powercontrol signal to the base station with a predetermined code sequence.2. The method for controlling the transmission power as claimed in claim1, wherein: the multi-point transmission target mobile stationdetermines contents of the transmission power control to be requested tothe base station on the basis of receiving quality of received signalfrom the base station, and transmits the transmission power controlsignal to the base station after spreading that signal with apredetermined code sequence when the contents of the transmission powercontrol is determined to be the increase request of the transmissionpower to the base station; and the base station calculates correlationbetween the signal received from the multi-point transmission targetmobile station and the predetermined code sequence pre-stored, andincreases the transmission power to the multi-point transmission targetmobile station if the correlation value exceeds a predeterminedthreshold and decreases the transmission power if the correlation valuedoes not exceed the predetermined threshold.
 3. The method forcontrolling the transmission power as claimed in claim 1, wherein: a setof the mobile stations consisting of the multi-point transmission targetmobile stations to which the base station transmits the same signal isreferred to as a multi-point transmission group; and the predeterminedcode sequence is different for each multi-point transmission group.
 4. Aradio communication system comprising a base station and a mobilestation where the base station is able to perform multi-pointtransmission for transmitting the same signal to a plurality of themobile stations, wherein: the mobile station targeted for themulti-point transmission provides the base station of an increaserequest or a decrease request of the transmission power by respectivelyspreading or not spreading a transmission power control signal to thebase station with a predetermined code sequence.
 5. A communicationterminal device acting as a mobile station communicating with a basestation in a radio communication system and comprising a transmissionpower control requesting part for requesting the base station toincrease or decrease the transmission power on the basis of receivingquality of received signal from the base station, wherein: thetransmission power control requesting part provides the base station ofan increase request or a decrease request of the transmission power byrespectively spreading or not spreading a transmission power controlsignal to the base station with a predetermined code sequence.
 6. Thecommunication terminal device as claimed in claim 5, wherein: upon beingtargeted for the multi-point transmission where the same signal istransmitted from the base station, the transmission power controlrequesting part uses, in code sequences provided to be different foreach multi-point transmission group, a code sequence assigned for themulti-point transmission group as the predetermined code sequence.